The field of the invention relates generally to electric motors, and more specifically, to electric motor controllers and methods of determining which of a plurality of motor controller input power lines has been energized.
A typical heating, ventilation, and air conditioning (HVAC) application includes a thermostat, a furnace or fan coil, a system controller, and a fan motor. User settings and current temperature measurements are used by the thermostat to provide the system controller with signals indicating the mode in which the HVAC application should operate. For example, a user may input into the thermostat a desired temperature of 67 degrees F. If the measured temperature of the room is 60 degrees F., the thermostat would signal the system controller to enter a heating mode.
The system controller energizes the fan motor via a set of relays based on the information provided to the system controller by the thermostat. Typically, certain known HVAC applications, such as residential HVAC systems, include a permanent split capacitor (PSC) electric motor to force airflow. The speed of the PSC motor is adjusted by taps on the motor winding. When the line voltage is applied to a lower turn count tap in the induction motor, the reduced stator flux produced results in a lower rotor speed under load, resulting in much inefficiency when using the PSC motor.
Some HVAC systems have begun using variable speed motors that can be electronically controlled to match the airflow requirements of the system to improve efficiency. However, retrofitting the PSC motor with a variable speed motor is costly, time-consuming, and requires complex changes to be made to the wiring and control system. Additionally, HVAC original equipment manufacturers (OEMs) typically require electric motors with unique parameters (i.e., torque, speed, airflow direction), so the motor can be customized to the particular system in which it is installed. Changing the operating parameters after manufacture is also a time-consuming and difficult process. As a result, electric motor manufacturers and installers keep an extensive inventory of motors to accommodate for the large variety of different HVAC systems.